1. Field of the Invention
The present invention relates generally to a process for forming an interlayer membrane for an electronic material using gaseous materials. Specifically, the present invention relates to a process for forming an interlayer membrane for a semiconductor device of which wirings are microrized and integrated, such as a memory device microrized and integrated. Alternatively, the present invention relates to an apparatus for forming such interlayer membrane.
2. Description of the Background Art
Recently, aluminum wirings formed on a semiconductor device has been more and more microrized and multilayered. Step difference between wirings and an interlayer insulating membrane present at a clearance of the wirings becomes larger and sharper according to such microrization and multilayering of the wirings, because the clearance becomes narrower. This causes deterioration of processing accuracy and reliability of the wirings. Therefore, flattening of the interlayer membrane laid on the wirings has been studied because step coverage of the wirings is difficult to be improved.
Conventionally, a chemical vapor deposition (hereinafter, a CVD) using an organic silane gas as one of a component of gaseous materials, for example, a plasma CVD, a vacuumed CVD and an atmospheric CVD, has been utilized to flatten an interlayer insulating membrane. Alternatively, variety of techniques have been utilized, such as configuring technique, e.g., bias sputtering and bias ECR-CVD, which chamfers the step of the wiring by sputter-etching during the membrane formation, coating technique to coat the membrane surface by an organic or inorganic spin on glass (SOG) membrane, and re-flowing technique softening the interlayer membrane by heat treatment to give flowability thereto. Etch back technique is also utilized to chamfer the step of the wiring for flattening.
When the techniques described as the above are applied to the wiring layer of microrized and multilayered, flattening of membrane at the wiring clearance of wide distance becomes not enough, and voids tend to be generated in the interlayer membranes at the clearance. Therefore, connection between wirings is deteriorated.
Flattening an interlayer insulating membrane on an aluminum wiring having high aspect ratio by the plasma CVD process using an organic silane of water added has been well known (refer to the 38th lecture scripts of the allied applied-physics institution, p 632, 29P-V-8 and 29P-V-9, 1991). However, when water is added, concentration of hydroxyl groups present in the membrane and that of by-produced alcohol are increased. Those cause certain increase of the rate of heat shrinkage during annealing resulted in crack generation on the membrane. Reliability of the multilayered wiring becomes deteriorated thereby.
Japanese Patent First Publication (not allowed) No. 3-116835 describes CVD using organic silane and inorganic acid as gaseous materials. Organic silane promotes hydrolysis reaction to reduce hydroxyl groups, and inorganic acid also reduces hydroxyl groups. However, when a proton donor, i.e., inorganic acid, is added, proton acts as a catalyst for hydrolysis to radically promote hydrolysis in the reaction system. This causes the concentration of hydroxyl groups in the system to be rapidly increased (refer to Journal of Non-Crystallin Solids, 63(1984), 13-21, North-Holland, Amsterdam). Shrinkage by the heat treatment and hygroscopicity of the membrane obtained are increased thereby.
Forming the membrane having high molecular weight allows the membrane to self-flow. Here, self-flowing is a phenomena of spontaneous flattening of the membrane free from specific flattening techniques. However, inorganic acid significantly increases the rate of hydrolysis in the system, therefore, product of low molecular weight causing inhibition of polymerization.
Additionally, in the conventional CVD process using a gaseous mixture, gaseous materials are sufficiently mixed prior to introduce in a reaction chamber to form the uniform membrane without delay. However, when a catalyst is added to the system, reaction between the catalyst and the gaseous materials is started immediately. Therefore, particles are formed in the conduit before the gases and the catalyst is introduced in the reaction chamber. Thus, membrane quality becomes deteriorated. Process for reducing desorption of the gases from the membrane has also been studied to raise membrane quality.